"Scientific and technical human capital" (S&T human capital) has been defined as the sum of researchers' professional network ties and their technical skills and resources [Int. J. Technol. Manage. 22 (7-8) (2001) 636]. Our study focuses on one particular means by which scientists acquire and deploy S&T human capital, research collaboration. We examine data from 451 scientists and engineers at academic research centers in the United States. The chief focus is on scientists' collaboration choices and strategies. Since we are particularly interested in S&T human capital, we pay special attention to strategies that involve mentoring graduate students and junior faculty and to collaborating with women. We also examine collaboration "cosmopolitanism," the extent to which scientists collaborate with those around them (one's research group, one's university) as opposed to those more distant in geography or institutional setting (other universities, researchers in industry, researchers in other nations). Our findings indicate that those who pursue a "mentor" collaboration strategy are likely to be tenured; to collaborate with women; and to have a favorable view about industry and research on industrial applications. Regarding the number of reported collaborators, those who have larger grants have more collaborators. With respect to the percentage of female collaborators, we found, not surprisingly, that female scientists have a somewhat higher percentage (36%) of female collaborators, than males have (24%). There are great differences, however, according to rank, with non-tenure track females having 84% of their collaborations with females. Regarding collaboration cosmopolitanism, we find that most researchers are not particularly cosmopolitan in their selection of collaborators-they tend to work with the people in their own work group. More cosmopolitan collaborators tend have large grants. A major policy implication is that there is great variance in the extent to which collaborations seem to enhance or generate S&T human capital. Not all collaborations are equal with respect to their "public goods" implications. (C) 2004 Elsevier B.V. All rights reserved.